In situ annealing procedures are to be used with I 125-transfer RNA to identify the sites of transfer genes on the polytene chromosomes of Drosophila melanogaster. The 5S ribosomal RNA cistrons will be located and compared amongst several species of Drosophila in an evolutionary study of the genomic placement of these cistrons. Amphibian lampbrush chromosomes are to be used with I 125 labeled nucleic acids to locate certain cistrons and satellite DNA sequences on the genome. An effort will be made to enhance the in situ annealing efficiency and to more fully quantitate the technique.